Selection of an aquatic indicator species to monitor organic contaminants in trophically simple lotic food webs.

A four-step procedure was used to identify an aquatic macroinvertebrate with which to monitor organic contaminant burdens in trophically simple lake food webs of Alberta, Canada. We identified leeches (Oligochaeta: Hirudinea) as the potential indicator assemblage (Step 1), and then documented their abundance and distribution in 16 lakes to identify a species-level bioindicator (Step 2). The latter two steps involved identifying the number and level of organic contaminants within the indicator species (Step 3) and a comparison with other taxa within the food web (Step 4).

Mortality, preference, avoidance, and activity of a predatory LeechExposed to cadmium.

The effects of cadmium on the hatching success of thecocoons of the freshwater predatory leech Nephelopsis obscura wereexamined together with the survivorship of hatchlings, changes in 96-hLC50 with biomass, preference-avoidance responses and changes inactivity. The 96-h EC50 for cocoons was 832.6 microg Cd/L with adecreasing bounded monotonic function best describing hatchling success as afunction of Cd concentration.